The management of cardiopulmonary bypass and temporary cardiopulmonary support systems has been long using equipment integrating a variety of medical devices, which are of similar types and also available as individually operating devices, which form as a whole an extracorporeal circuit.
These apparatus, also known as heart-lung machines, use extracorporeal circuits having a considerably low degree of integration with the apparatus.
This has the main purpose of allowing users to use a common apparatus, to be equipped with disposable devices mounted and used thereon, which have equivalent performances but are produced by different manufacturers, and allowing users to adapt a circuit to their own requirements and available spaces.
A disposable extracorporeal circuit typically comprises venous and arterial cannulas which are placed by surgery or percutaneous methods on a vascular access of relevant size, e.g. the venae cavae or the femoral vein for the venous section and the descending aorta or femoral artery for the arterial section.
These cannulas form the interface between the disposable circuit on the apparatus and the patient.
The circuit is composed of a tube that drains blood from the patient, also known as venous return, a soft container (bag) or a rigid container, a venous reservoir for collecting blood from the patient, a pump, an oxygenator with an integrated heat exchanger, an arterial filter and a number of tubes for interconnecting these elements and allowing easy filling and monitoring thereof during use.
Nevertheless, the possibility of using a variety of devices with a single apparatus limits integration of the various disposable devices and increases the likelihood of inducing errors in their use, with the risk of affecting patient's safety.
Particularly, air may enter the extracorporeal circuit from a number of points, typically from the venous cannula, or from the many connections between extracorporeal tubes interconnecting the various devices of the circuit, or due to not easily predictable intra-operative events.
Therefore, there is the need of minimizing the ingress of air into the blood circulating in the extracorporeal circuit, by removing it before it reaches the last elements of the circuit (namely the heat exchange and the oxygenator) to prevent hazardous events for the patient.
In clinical practice, both venous and arterial cannulas shall be entirely filled with the patient's blood, whereas a blood biocompatible filling solution, typically a saline or another electrolyte-rich solution is used to fill the entire extracorporeal circuit, before coupling the cannulas filled with the patient's blood to the circuit filled with such solution. The blood volume and/or biocompatible solution pumped into the circuit is known as “priming volume”.
Typically, the whole extracorporeal circuit is “washed” with CO2 before being filled with the above mentioned solution, because this gas (i.e. carbon dioxide) both simplifies removal of air from the circuit, and dissolves more easily in the filling solution.
Then, such filling solution pushes the “washing” CO2 out of the circuit and facilitates full removal thereof.
Next, once the whole circuit has been filled, and any air and micro-bubbles have been removed, blood flow is started by opening the venous cannula whereupon, as soon as blood starts to flow within the circuit, the arterial cannula is also opened.
The circuit volume should be minimized, because the filling solution dilutes the patient's blood, thereby impacting his/her hemodynamic conditions.
In an attempt to obviate the above drawbacks, circuits with smaller and smaller volumes have been developed which, in spite of the resulting reduction of air trapping devices, were found to achieve the same effectiveness, by using more or less automatic systems for quickly blocking and removing air from the circuit, possibly without requiring any action by an operator for this delicate and critical operation, which is required to ensure safety against accidental ingress of air into the circuit and hence into the patient, and thus avoid any possible gas embolism.
This necessarily involved an evolution of the apparatus designed to manage these mini-circuits, which should ensure a considerable degree of integration between disposable devices and hardware and software devices.
Such an apparatus is disclosed by Patent Application US2006/0122551A1, in which the entire disposable circuit is pre-assembled into some sort of cartridge, which is precision-fitted into a specially designed apparatus.
In terms of structure, this apparatus uses the prior art technique as used for closed-loop cardiopulmonary bypass, in which a soft reservoir, typically consisting of a deformable bag, collects the venous blood from a patient, a centrifugal pump draws and conveys it to an oxygenator having an integral heat exchanger.
Then, the pump thrust conveys blood from the oxygenator to an arterial filter and then, via a tube, back to the patient.
The “patient” module as disclosed in the patent comprises a series of separate elements, which are assembled together to a minimized size on a support frame that forms some sort of cartridge, adapted to be mounted to the apparatus using preset interfaces, that engage the cartridge in the priming position.
The peculiar feature of this device is that during the priming step the whole circuit is oriented along an axis that facilitates removal of air from the disposable device.
Once priming has been completed the cartridge rotates integrally with a portion of the apparatus, indicatively through 90° from the priming position and prepares for use with the patient.
Patent Application US2007/0009378A1 discloses a device for control of extracorporeal blood circulation, which comprises at least one oxygenator, a heat exchanger and a blood filter, having the inlet and outlet connections of the oxygenator/heat exchanger so incorporated that blood flow has a hydraulic section of 80 mm2 or more or preferably 120 mm2 or more.
The disclosed device may operate both separately and as a structural part that combines the operations of an oxygenator, a heat exchanger and a blood filter.
Patent Application US2009/0175762A1 also discloses a device for control of extracorporeal blood circulation, which comprises at least one venous reservoir, a centrifugal pump, an oxygenator, and means for interconnecting them into a structural unit that combines the operations of an oxygenator, a heat exchanger and a blood filter.
This patent discloses a device that separates air from the patient's blood, which is drained by the negative pressure created by the rotation of a centrifugal pump.
A bubble removing device is placed between the patient's blood drainage line and the centrifugal pump and is interfaced via a special sensor to a regulating unit.
The above described prior art suffers from certain drawbacks.
A first drawback is that prior art heart-lung apparatus use water-supplied/thermostated heat exchanger devices. Therefore, for proper operation they must be combined with large apparatus, such as thermostated baths or thermostated reservoirs, that are not easily transportable.
Since prior art heat exchangers rely on a source of a temperature-regulating fluid, operators must carry patients with cardiogenic shock or serious cardiopulmonary failure caused by an acute event, such as myocardial infarction or post-traumatic hypovolemia, from the place where injury occurs to the hospitals in which heart-lung machines are available and stably connected to such sources of temperature-regulating fluid.
This involves a critical time loss, before starting treatments for rescuing the patient.
A further drawback is that patient aid only generally relates to circulation, hence artificial aid in cardiac output and the associated lung function, using pumps and an oxygenator, without using, for instance, induced and/or controlled hypothermia, to keep the brain and heart functions of the patient unaltered and as effective as possible.
Another drawback is that physical parameters, such as pressure and temperature are monitored using probes and electric cables that are directly connected to the apparatus but are not ergonomically integrated thereon, which is a limit both in terms of system preparation times, as well as in system completeness and compactness.
A further drawback is that prior art systems do not include integral apparatus for monitoring hematochemical parameters, such as pH, partial pressures of O2 and CO2, which are critical parameters for proper therapeutic treatment and which can only be detected by combined use of special auxiliary instruments.
Yet another drawback is that prior art systems do not include integrated oxygen or pre-mixed gas bottles for ventilation of the oxygenator units used by these systems.
Therefore, the system cannot be adequately used in cases of emergency, or when patients have to be transported in critical conditions, unless combined use is made of auxiliary instruments which have a large size and are not easily transportable.